Current state of the art composite large aircraft wing spars are typically manufactured from prepreg materials with Automated Tape Laying (ATL) and then hot formed to the desired shape over a male mandrel. The spar is then cured either on a male tool or in a female tool. Prepreg manufacture requires the use of an autoclave, which is a large capital investment. Also, the ATL process is only able to build a relatively simple structure with small thickness variations, simple pad-ups and shallow ramps, and any folding lines being more or less straight. More complex geometries and fibre architectures require the prepreg to be laid manually or with the use of fibre placement.
An alternative process for manufacturing a composite component is so-called Resin Transfer Moulding (RTM) in which dry fibre is infused with liquid resin between a rigid male and female mould tool. Conventionally, where a complex geometry is required, then the dry fibre is laid by hand into the female mould tool. This manual lay-up process is laborious and time consuming.